The present invention relates to an improvement in anti-icing systems for aircraft jet engine propulsion systems.
The formation of ice on aircraft wings, propellers, air inlets of engines, etc. has been a problem since the earliest days of heavier-than-air flight. Any accumulated ice adds considerable weight, and changes the airfoil or inlet configuration making the aircraft much more difficult to fly and in some cases has caused loss of aircraft. In the case of jet aircraft, large pieces of ice breaking loose from the leading edge of an engine inlet housing can damage rotating turbine blades or other internal engine components and cause engine failure.
One of the most common anti-ice techniques has been the ducting of hot gases into a housing adjacent to the likely icing area. Current techniques to solve this problem generally fall into one of two types of systems: Impingement style ring systems or swirl nozzle systems. In each case, the hot gas conduits simply dump hot gases into a housing, such as the leading edge of a jet engine housing or a wing leading edge. While often useful, these systems are not fully effective due to the low quantity of hot gases introduced relative to the mass of air in the housing, the heating effect tending to be limited to the region near the hot gas introduction point, and the complexity of the hot gas duct system.
In impingement style ring systems, hot air is impinged on the metal lipskin by strategically positioned holes in an annulus shaped tube that runs 360 degrees around the front of the inlet. The air impinges on the internal lipskin surface and causes the metal temperature to increase and break off any ice accretion.
The existing swirl nozzles discharge the hot air through a few non-circular sub-nozzles that create a flow field. The air is discharged at a high velocity so that it creates a swirling effect in the forward most inlet compartment, commonly referred to as the D-duct. The air continues to move 360 degrees around the annular D-duct compartment. It circulates around the compartment several times until it exits into the ambient through an exhaust port. Since the inlet lipskin consists of most of the internal compartment surface area, the hot air heats the lipskin and causes any ice accretion to break loose. Although the figures and verbiage of the specification use nose cowl deicing for explanatory purposes, the invention disclosed herein may apply to any other housing subject to ice formation including, but not limited to, wing conduits and ducts.
Both systems have limitations. The impingement ring style anti-ice systems have a cumbersome tube and support structure that runs 360 degrees around the front inlet compartment. While these systems generally have very high heat transfer ratios they are also very heavy. Swirl nozzle systems are generally significantly lighter than impingement ring style systems and use less air to de-ice but suffer from lower heat transfer.